Rhopalonema velatum Gegenbaur, 1857

Buecher, Emmanuelle, Goy, Jacqueline, J, Mark & Gibbons, 2005, Hydromedusae of the Agulhas Current, African Invertebrates 46, pp. 27-69 : 36-37

Rhopalonema velatum Gegenbaur, 1857

Rhopalonema velatum: Gegenbaur 1857: 251 , pl. 9, figs 1, 5; Kramp 1961: 262; 1968: 115, fig. 307.

Description: 131 specimens from 57 stations. Bell-shaped umbrella, as tall as broad; up to 15 mm in height; with a distinct round apical projection. Exumbrella surface smooth. Mesoglea thickened at apex, thinning laterally. Velum broad. Peripheral canal and eight radial canals present; no centripetal canals between radial canals. Eight tentacles, each arising from umbrella margin opposite radial canal (perradial), long(ish), hollow and with a terminal swelling. Eight secondary tentacles at umbrella margin (one per octant), cirrus-like, short, stiff (frequently lost on preservation). Manubrium cylindrical, elongated and reaching almost to level of velum. Mouth with four simple lips, without gastric peduncle. Up to 16 statocysts present; situated at base of each tentacle and cirrus. Eight gonads, oval or linear in shape, each arising from subumbrella surface, attached for full length, extending along middle 1/3 radial canal.

Material examined: H5001, H5002, H5003.

Comments: The only other valid species in the genus, R. funerarium Vanhöffen, 1902 , has also been caught in the tropical Indian Ocean (Kramp 1957). It can be separated from R. velatum by the absence of an apical projection, a shorter manubrium (not reaching to level of velum) and by the relative position of the gonads (along the distal 2/3 of the radial canals).

Distribution: World-wide in tropical and warm temperate waters. Previously caught off the Chagos Archipelago (Browne 1916) and Mozambique (Bouillon 1978 b). Epipelagic.

Class Hydroidomedusa Claus, 1877 emended

Subclass Anthomedusae Haeckel, 1879

Family Bougainvillidae Lütken, 1850

Bougainvillia fulva Agassiz & Mayer, 1899

Bougainvillia fulva: Agassiz & Mayer 1899: 162 , pl. 2, fig. 6; Kramp 1961: 77; 1968: 33, fig. 84.

Description: Nine specimens from 8 stations. Essentially cylindrical umbrella, slightly taller than broad, up to 13.5 mm high. Exumbrella surface smooth. Mesoglea thick, especially near apex. Peripheral canal and four radial canals present. Tentacles borne in four clusters, each cluster arising from narrow, epaulette-shaped bulb at umbrella margin opposite radial canal (perradial); 12–15 tentacles per cluster, short, solid and with a very slight terminal swelling. Secondary tentacles absent. Manubrium wide, flat. Mouth simple, circular; without gastric peduncle; bearing four oral tentacles above mouth rim. Oral tentacles dichotomously branched 8 times; small, with terminal cnidocyst clusters. Without statocysts. Ocelli black, minute, situated at base of each tentacle. Eight oval distinct, adradial gonads, situated on manubrium.

Material examined: H5004, H5005, H5006.

Comments: Although only 23 species or so of medusae are considered valid by Bouillon and Boero (2000 b), the number of described forms greatly exceeds this. Species can be separated with difficulty using a combination of features—the size and shape of tentacular bulbs, the number of tentacles per marginal bulb, and the number, size and colour of associated ocelli. The length and rigidity of marginal tentacles can also be useful in distinguishing species, as can the degree of branching and the point of first branching of the oral tentacles (and whether they are capitate or filiform). Aside from B. muscoides (see below) two other species of Bougainvillia medusae have been tentatively identified from the west Indian Ocean: B. platygaster (Haeckel, 1879) (Kramp 1957, 1965; Bouillon1978 b) and B. muscus (Allman, 1863) ( Millard 1975; Bouillon 1978 b). B. platygaster has triangular tentacular bulbs bearing 10–13 slightly capitate tentacles and four crescent-shaped ocelli; its small oral tentacles are capitate and dichotomously branched from the base, 4–5 times. B. muscus is globular and has small oval tentacular bulbs supporting 4–9 slightly capitate tentacles and minute black ocelli; its small oral tentacles are capitate and dichotomously branched above a distinct base, only twice. B. macloviana (Lesson, 1830) was collected by Bouillon (1978 b) off the Seychelles archipelago.

Distribution: Widely distributed in tropical and subtropical waters of the Pacific and Indian Oceans. Previously caught off the Chagos (Browne 1916) and Seychelles archipelagos (Bouillon 1978 b), and along the east coast of South Africa ( Millard 1975). Neritic.